I have a few friends i hang out with who ask me to help them out, either outright before the fact or thru eye contact and facial expressions in the moment.
I employ a few methods for dealing with these guys, and most of them are situational and depend on my read of the guy. For a guy who is seemingly drunk or seems to be potentially hot headed, i never turn my back to him. I will however put myself between him and the girl, but instead of "blocking" him i put myself between so i have his attention (usually intro myself with a handshake and strong ec). Then i use a combination of words and strong ec.Dependant on the guy i may try to "befriend" him and then get him to go away, or i might just be a dick and blow him out.
I save physical contact as a last resort, altho sometimes it seems putting your hand(s) on them is the only way to get the point accross, ranging from seemingly friendly to dominant to aggressive contact.
The girls appreciate it, it looks good to outsiders for you, and most importantly it keeps the girls close to you (at least within eye contact).